Skywatch January 2002

These scripts are written by members of the Albany Area Amateur Astronomers and read by the staff of the Dudley Observatory. All scripts are copyright and may not be reproduced without permission of the writer and the Dudley Observatory. Scripts are published to the web in the week following their recording. Daily scripts may be heard by calling 518-382-7584 after 5pm.

 

 NOTE: Times given in the scripts are all local Schenectady, New York time.

Tuesday, January 1st. Written by Jonathan Cassidy.

The stars Betelgeuse & Rigel are same brightness and roughly the same distance. These two stars can be seen as the brightest stars about the same distance to the left and right of Orion's belt stars. The belt stars stand straight up from the eastern horizon between 8 & 9 PM.

Close examination will show that there is a significant color difference between these two stars. This can be seen even from light polluted city sites. Betelgeuse is red/white and Rigel is blue/white. Rigel is truly brilliant and burning very hot. Betelgeuse is, by comparison, cool and dim.

Why then do they look about the same brightness? The answer is size. Betelgeuse is a huge red giant. If it were at the center of our solar system the outer atmosphere would be near the orbit of Jupiter. It is its size that makes it look brighter. The red color means it has burned most of it's Hydrogen fuel and is now burning heavier materials. Hydrogen burns the hot. The blue tinge to the color is an indicator of hot temperature and the primary fuel is Hydrogen. Red color indicates that heavier elements are being burned at a lower temperature.

Betelgeuse is an old star and is nearly burned out. Rigel will never get very old as it is burning too fast and will burn out in a short time, hundreds of millions of years instead of billions.

Wednesday, January 2nd. Written by Ray Bogucki.

An interesting coincidence today places the Moon at perigee, its closest approach to the Earth in its elliptical monthly orbit, and places the Earth at perihelion, our closest approach to the sun in our annual orbit. The light from the almost-full Moon has seemed a bit brighter than usual this week for a collection of reasons. Our nearness to the Sun means that the sunlight striking the surface of the Moon and reflecting back to the Earth is somewhat brighter than usual. Also, because the Moon is 25,000 miles closer to us today than it was at apogee two weeks ago, its disk appears both larger and brighter than normal.

While the bright moonlight may be an advantage for travelers making their way at night, it is a distinct disadvantage for meteor watchers awaiting the Quadrantid meteor shower tomorrow. Although the Quadrantids may produce almost as many meteors per hour as the Perseids or Geminids, they are less well known, probably because the weather in January tends to be frigid and cloudy, and not conducive to long periods of observation. The Quadrantids have a short period of peak activity lasting a few hours at most. Unfortunately the peak is expected about 1 p.m. tomorrow, but there should still be some activity at nightfall and past observations of bright blue meteors with long trains may provide an incentive to go out and watch. The best time to observe will be early in the evening before the bright moonlight washes out the fainter meteors.

Unlike most meteor showers whose parent comets or asteroids are well known, the source of the Quadrantids is a mystery. Some astronomers believe that the parent comet was captured by Jupiter or collided with another body long ago and was destroyed, while its trail of debris continues to orbit the Sun. Others argue that the debris stream belongs to an existing, recurring comet which has not returned or been observed in recent times.

Thursday, January 3rd. Written by Peter Jennes.

Sunset for tonight, Thursday, January 3rd was at 4:34. At sunset, Mercury is beginning a two-week climb into the evening sky. During this climb, Mercury will pass about two degrees south of Neptune on January 9th. At magnitude -1, Mercury is relatively easy to spot against the sunset glow. However, at eighth magnitude, Neptune will be extremely difficult to spot. The best visibility for Mercury during the next two weeks will be within a few days of the 15th. At that time, Mercury will be about 10 degrees above the horizon as the sky gets dark. Since sunset occurs at 5:07 on the 15th, astronomical twilight will not end until just before 6 PM on that date.

As Mercury is setting and the sky is getting truly dark, the brightest star of the Northern Hemisphere, Sirius will be rising. Aside from its brilliance, Sirius is easy to spot because the Belt of Orion points almost directly down to it. Since Sirius is located 20 degree below the celestial equator, it is visible from nearly every populated region of the Earth. Interestingly, many of these people imagined the outline of a dog in the stars around Sirius. To the Greeks, these stars were Orion's hunting dog. The Scandinavians saw Sigurd's dog and in India, these stars were called the Deerslayer.

Now, thanks to the power of modern scientific instruments, we know that these stars have nothing to do with dogs. Instead, an amazing list of observational discoveries has replaced the Sirian legends. However, before those legends died, one last legend made its way into scientific fact. In this story, the Finnish poet, Topelius, imagined Sirius' great brilliance was due to the combined light of two stars that he represented as lovers meeting and embracing in the stanza:

Straight rushed into each others arms
And melted into one,
So they became the brightest star
In heaven's high arch and dwelt
Great Sirius, the mighty sun,
Beneath Orion's belt.

Later, the German astronomer Bessel used ten years of observations to predict that Sirius was in fact a double star. This prediction was based on periodic variations in Sirius' motion, and in 1862, Alvin Clark used Bessel's very accurate predictions to spot the tiny white dwarf companion of Sirius.

Friday, January 4th to Sunday, January 6th. Written by

Monday, January 7th. Written by Susan C. French.

If you go outside at about 6 PM, you will see the constellation Taurus, the Bull, 40 degrees above the eastern horizon. (A fist held at arm's length spans about 10ƒ across the knuckles.) The face of the Bull is framed by a V-shaped group of stars that will be lying on its side. The point of the V is to the right, and the open end is to the left. The dimmer stars of the Bull's face form a star cluster known as the Hyades (HIGH-ah-deez). It is one of the closest star clusters to Earth at a distance of about 130 light years or 780 trillion miles. Through binoculars, about 25 bright stars and many fainter ones may be seen in the Hyades. Several stars are bright enough to show some color, and the cluster contains some nice double stars.

Two bright objects can be seen in the V. In the lower arm, you can see the orange star Aldebaran, which marks one of the Bull's eyes. Aldebaran is a giant star about 40 times bigger across than our sun and 125 times more luminous. It is not a member of the Hyades, but a foreground star lying about 68 light years or 408 trillion miles away.

The second bright object lies in the upper arm of the V, giving the Bull a somewhat misplaced second eye. This is the planet Saturn, which is now slowly wandering through the Stars of Taurus. Saturn is most well known for its beautiful, bright rings. Through a small telescope, Saturn displays a single, bright ring that spans over twice the diameter of the planet itself. Larger telescopes may reveal some divisions in the rings and some detail on the planet.

Another star cluster can be spotted about one "fist" above the Hyades. This group is known as the Pleiades, or Seven Sisters. Many people mistake the Pleiades for the Little Dipper. It does have a dipper shape, but the Little Dipper is a much larger star pattern which is always located due north. Although the cluster is often called the Seven Sisters, many people can only count six stars here while others claim to see as many as 17. If you look at the Pleiades with binoculars, you will find that the cluster contains many more stars than you can see with your eyes alone. Once you have located some of the brighter stars with binoculars, see if you can use this knowledge to increase your naked-eye count.

Tuesday, January 8th. Written by Jonathan Cassidy.

The waxing crescent Moon leaves us with mostly stars and planets tonight and all this week. Elusive Mercury will put on its best show late in the week. It will appear 19 degrees above the western horizon at sunset on Friday.

When Mercury is east of the Sun we see it in the evening. When it is west of the Sun we see it in the morning. Mercury is very difficult to spot due to its tight orbit around the Sun. Fortunately its closeness to the Sun makes it bright by reflection. It will be the only thing very low in the western sky after sunset. Anyone with a good western horizon will be able to see if the weather is clear. It will set about 40 minutes after the Sun. Binoculars of any size help locating Mercury.

Mercury takes just about two months to make an orbit of the Sun. Thus we should be able to see three evening and three morning appearances each year. However Mercury most times does not stray so far from the Sun, or the angle makes the separation appear smaller.

This makes the appearance of Mercury this week all that more special. The early May evening setting of Mercury may be better, but that appearance will be over shadowed by the glitter of neighbor, Venus climbing in the west for it's best show a month later. So catch Mercury while it is the only show in town in the west this week.

Wednesday, January 9th. Written by Ray Bogucki.

This is a good week to catch sight of our innermost and most elusive bright planet Mercury. Tonight it reaches maximum brightness during its current apparition as an evening star. Friday night it will be at its greatest elongation, 19 degrees east of the Sun. Look for Mercury low in the west-southwest at twilight. Next Tuesday evening it will be easy to find, shining with a magnitude greater than zero and lying about 10 degrees to the right and a little below the new crescent Moon.

Moving from the smallest inner planet, Mercury, to the largest outer planet, Jupiter, we note that Jupiter stood at opposition last week, meaning it is just opposite the Sun as seen from Earth. Thus Jupiter rises in the east as the Sun sets in the west, and sets as the Sun rises. Because we are at our closest approach to Jupiter for this orbital cycle, it appears especially large, at 47 arc-seconds in diameter, and especially bright, at magnitude minus 2.7. From its location in the constellation Gemini, it completely dominates the night sky, shining 3 times brighter than the brightest star, Sirius.

Jupiter made history on Jan. 7, 1610, when Galileo became the first human to behold the four bright moons of Jupiter and quickly realized they were orbiting the giant planet. This was the first direct evidence of a gravitational center in the Solar System other than Earth, the only center in the old Ptolemaic system. The publication of Galileo's observations lent crucial support to the sun-centered system proposed by the Polish astronomer Copernicus, 67 years earlier. Galileo was later condemned by the Church for heresy, and on yesterday's date in 1642, he died, leaving an incredible legacy in the development of telescopes, microscopes, the pendulum as a timing device, the laws of motion of falling bodies, practical uses of magnetism and in many other areas. His lifelong practice of recording his observations in careful detail laid the foundation of modern scienctific practice.

Thursday, January 10th. Written by Peter Jennes.

  Sunset for tonight, Thursday, January 10th was at 4:41. The moon is just three days away from new and the sky will be dark for the entire night. By the time the sky is completely dark, the bright star Capella will be high above the northeastern horizon. Capella is not only the brightest star in the constellation of Auriga, it is also fourth brightest star in the northern hemisphere and the sixth brightest star in the sky. The only other stars that are brighter than Capella in our northern skies are Sirius, Arcturus, and Vega.

At nearly zero magnitude, Capella is a dazzling yellow star. To spot it, go outside around 7 PM, at that time, Capella will be about 60 degrees above the northeastern horizon. In light polluted urban areas, Capella will be unmistakable since it will be the brightest star shining through the urban skyglow in that region of the sky. In fact, Capella is the most northerly of stars brighter than first magnitude.

Besides being such a bright star, Capella is interesting for other reasons. Capella is actually a double or binary star. Both components of this system are about the same temperature as our own sun but they are many times larger and brighter. Astronomers speculate that the stellar components of Capella are either approaching the red giant stage of their life or are contracting from that stage. Red giant stars have nearly exhausted their nuclear fuel and are approaching the end of their life.

Capella is about 45 light years away making it relatively nearby. However, even though Capella is almost our next door neighbor, it is all but impossible to resolve the two stars that make up this system. Only by using an instrument known as an interferometer can astronomers measure the distance between the stars of Capella. The separation determined with the interferometer is a scant 70 million miles. With this small of a separation, the stars of Capella orbit around each other in about 104 days. When double stars are this close, they are called spectroscopic binaries because fluctuations in the star's spectrums usually lead to the discovery of their binary nature.

Friday, January 11th to Sunday, January 13th. Written by

Monday, January 14th. Written by Susan French.

Orion, the Hunter, is the brightest constellation in the sky, and it is now visible due south at about 10 PM. Many novice stargazers find the belt of Orion one of the most striking asterisms in the sky. It is formed by three identically bright stars in a straight line. At 10 PM, the line slants slighty from the lower left to the upper right. This pattern may be distinctive, but it does not hold the brightest stars of the Hunter. Orion's brightest star is Rigel (RYE-gell), which marks one of the Hunter's knees. It can be seen to the lower right of the belt, while Saiph (saw-EEF), Orionís other knee, will lie to the lower left. The distance to Rigel is poorly known but is probably around 900 light years or 54 hundred trillion miles. To appear as bright as it does from such an immense distance, Rigel must be about 55 thousand times brighter than our sun.

Orionís second brightest star is Betelgeuse (BET'L -jews), which marks one of the Hunter's shoulders. It lies to the upper left of Orion's belt, while Bellatrix (bell-LAY-trix), Orion's other shoulder is to the upper left of the belt. Betelgeuse is one of the largest stars you can easily see with the unaided eye, and it is variable in size. If you put Betelgeuse where our sun is, it would engulf the Sun, Mercury, Venus, Earth and Mars at its minimum. At maximum, Betelgeuse would fill a sphere with the diameter of Jupiter's orbit. Together, the shoulder and knee stars form the corners of a large rectangle with the Orion's belt stars in the middle.

Once you've identified the stars, try comparing the colors of Rigel and Betelgeuse. Our eyes can distinguish colors only in the brightest of stars. Betelguese has an obvious reddish-orange tint, while Rigel is white with subtle overtones of blue. These colors indicate the surface temperatures of the stars. Rigel is one of the hottest stars in the sky while Betelgeuse is one of the coolest. Good binoculars can help reveal the colors of the stars, and work even better when the stars are slightly defocused.

A large, loose, star cluster known as Collinder 70 surrounds and includes the stars of Orionís belt. The group spans about 3 degrees and includes 100 stars, many of which are visible through a pair of binoculars. The field-of-view of most binoculars is between 5 and 10 degrees.

Tuesday, January 15th. Written by Jonathan Cassidy.

Watch the Moon pass by Mars this week. We have several planets up in the night sky now. Mars in the west, Saturn and Jupiter in the east. All the major objects of our solar system, planets; Moon and Sun, travel a similar line in the night sky. This line is called the Ecliptic. All of the objects vary a little from this line but never stray far from it. This is because our Moon, the planets and the Sun are all aligned in orbits that are in nearly the same plane.

Thus in turn they all come close to each other at one time or another. This week between Saturday and Sunday night our Moon will come quite close to Mars. Though there are millions of miles separating them they will appear to be next door neighbors these two nights. Then the Moon will seem to loose interest and move on to other brilliant objects. Mars is left to fade alone in the west, till next month's visit from the Moon.

If you were on the surface of the planets Uranus or Saturn, you would not see the local moons travel along the path of the Sun as they do not move in the same plane but have inclined orbits. Close encounters are few and far between.

Wednesday, January 16th. Written by Ray Bogucki.

For the next two months, the eastern evening sky will present its display of the brightest constellations in the annual progression. Whereas the summer sky has its famous Summer Triangle of three bright stars, the winter sky has its equivalent in the Winter Hexagon defined by the six bright stars, Sirius, Procyon, Pollux, Capella, Aldebaran and Rigel. A line drawn on a star chart connecting these stars, in order, produces a very credible hexagon which also includes Castor, the twin of Pollux and, in the center, the bright red supergiant Betelgeuse, in the left shoulder of Orion the Hunter. Adding to the brilliance this winter are the two visiting bright planets, Jupiter and Saturn. With Mars receding and growing fainter, and Venus passing behind the Sun, these two gas giants are currently the brightest planets in the sky. Jupiter shines from the center of Gemini, while Saturn sits in the face of Taurus the Bull, across from Aldebaran, the red eye of Taurus, temporarily providing the Bull with a second eye.

The constellation Taurus is notable for containing the two largest and brightest open star clusters in the Northern hemisphere easily visible to the naked eye. The better-known of the two is the Pleiades, a tight little cluster in the Bull's shoulder a few degrees west of Aldebaran, and often mistakenly called the "little dipper". These hot young stars present a splendid sight in binoculars, sparkling with blue-white intensity. Unlike some close star groupings which coincidentally lie along our line of sight but are actually not connected, this is a true association of stars. Born at the same time from the same cloud of interstellar gas a few tens of millions of years ago, they move together as a group. As a correlation in time, it's interesting to consider that the dinosaurs never saw these stars because they had not yet formed when the dinosaurs became extinct.

The second cluster is the Hyades (HIGH-a-deez), forming the "V" shape of the Bull's face below Aldebaran. Also a striking group of hot young stars, the Hyades have no connection with the Pleiades, which are approximately 100 light-years farther away from us.

Thursday, January 17th. Written by Peter Jennes.

By 8 PM, the bright star Capella is almost directly overhead. Capella is 42 light years away and over 150 times as bright as our Sun. After traveling 250 trillion miles to Earth, the light from Capella dims to 0.1 magnitude. However, Capella is still the sixth brightest star visible from Earth. Capellaís brilliance makes it relatively easy to find the triangular asterism of third magnitude stars about 3.5 degrees away from the stellar beacon. The triangle is about 2.5 degrees on two sides and less than one degree wide at the bottom.

Capella and its nearby asterism both belong to the constellation Auriga. Auriga is an ancient constellation and over the ages, great changes have been made to the mythology associated with the constellation. Early civilizations along the Euphrates River used the constellation's stars to tell the story of a shepherd. Later civilizations used the same stars to make a chariot and charioteer and from that story we get the name of the constellation. Despite thousands of years of changes, fragments of the shepherd's story still exist in the triangle of stars near Capella. To this day, the asterism is still called "the Kids" in reference to an era when the three stars were baby goats held in the shepherd's arm.

Although the stars of the Kids asterism look like they are closely associated, observations prove these similarities are just an illusion. For instance, Epsilon Auriga is the vertex closest to Capella. Epsilon is over 4,000 light years away and one of the most bizarre eclipsing binary stars known. Every 27 years, Epsilon undergoes a two year eclipse that dims the star by nearly one magnitude. Astrophysicists have derived several models that try explain this system but none of them are fully satisfactory. One theory invokes the existence of a giant companion star with the consistency of empty space while another calls for an off center dust disk surrounding the main star. At the bottom of the triangle, the brighter star is a white, B-type star 400 times brighter than our Sun and about 200 light years away. The dimmest star of the asterism is another eclipsing binary over 500 light years away which means the appearance of this asterism is just a chance alignment of stars.

Friday, January 18th to Sunday, January 20th. Written by

Monday, January 21st. Written by Joseph Slomka.

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